1. Field
The present disclosure relates generally to carbon nanotube technology and the like, and more particularly to carbon nanotube array bonding.
2. Background
Vertically-aligned carbon nanotube (VACNT) arrays, sometimes referred to as VACNT “forests,” have recently garnered attention for a variety of applications across different industries. In the energy storage industry, for example, VACNT arrays may be attached to current collector metal foils and used as battery electrodes. VACNT arrays offer an attractive platform for hosting anode and cathode active materials, such as Lithium in Li-ion battery cells. Improved battery electrodes are essential for high power applications in low- or zero-emission hybrid-electrical or fully-electrical vehicles, consumer electronics, energy-efficient cargo ships and locomotives, aerospace, and power grids. In the semiconductor industry, as another example, VACNT arrays may be integrated into various metal heat sink arrangements and used to improve heat dissipation by increasing the surface area in contact with a surrounding cooling medium. Improved heat dissipation is critical for modern and future semiconductor devices as power consumption and circuit densities continue to increase.
Widespread adoption of such devices has been impeded, however, by the heretofore inadequate conductor-VACNT interface structures in conventional designs. Conventional bonding techniques for attaching VACNT arrays to conductor surfaces of interest have in fact been one of the primary factors limiting performance. Many conventional designs attempt to grow VACNT arrays directly on metal surfaces as part of an in situ fabrication procedure. This approach suffers from several shortcomings as metal surfaces are not well-suited for use as carbon nanotube substrates. In particular, these structures tend to produce carbon nanotubes of poor quality and limited length. In most instances, the maximum achievable length is only on the order of about 100 nanometers or less.
Growing VACNT arrays on ceramics such as quartz, for example, provides for a more controlled fabrication process and produces better quality carbon nanotubes in the VACNT array. However, conventional techniques for transferring such VACNT arrays, once produced, to conductive surfaces of interest rely on materials that provide poor performance or are limited in their application (or both). For example, conventional bonding techniques in the semiconductor industry often use soft metals (e.g., gold) to interface VACNT arrays with metal (e.g., copper or aluminum) heat sink surfaces. The soft nature and typically low melting points for these materials facilitates bonding. For the same reasons, however, these materials are not well-suited for high-temperature applications. In addition, in some cases Li ions or other electrolyte species of Li-ion or other batteries may react with the underlying metals, causing corrosion or other type of degradation. This may limit or prevent the use of soft metal intermediate layers between VACNT and conductive current collector surfaces in many electrochemical energy storage applications.
High thermal and electrical conductivity of electrodes is desired for many energy storage applications because most of the battery degradation mechanisms have strong temperature dependencies. Local heating caused by moderately high current pulses may severely diminish battery cycle life. Sophisticated methods of thermal management that employ microfluidic channels incorporated within the battery to transport cooling fluids have been proposed to address this issue, but these approaches dramatically increase the cost and complexity of battery production. In semiconductor devices, there is an additional demand to remove heat efficiently from various junctions and to do so at elevated temperature. This demand is currently not met.
Accordingly, there remains a need in the art for improved conductor-VACNT interfaces and related methods of manufacture so that the full potential of VACNT-based devices may be realized.